1. Field of the Invention
The present invention relates to a landing mat for use in gymnastic exercises and together with a horizontal bar, parallel bars, uneven bars, a long horse, a pommel horse, flying rings, a balance beam or the like.
2. Technological Background
The mats of this type must be designed to ensure safe landing for gymnasts and assist them not to totter on the mat but to stand still and upright. The first function of ensuring safe landing relies on the capability of absorbing the shock imparted to those who are landing. The second function of helping them to their upright posture is the possibility of evenly receiving a dynamic load so as to prevent any portions of their feet from sinking deeper than the other portions.
These functions may be evaluated using the following three parameters (a)-(c) in combination.
(a) FO-max (viz. `ef-ou max`) PA1 (b) S-ein (viz. `es-ain`) PA1 (c) S-ruck (viz, `es-rak`)
This parameter in the terms of `N` (viz. newtons) is called the `shock damping coefficient` or `maximum break force` for bearing an impact stress loaded on the landing mat. An extremely high FO-max value represents, for example, a landing on a very hard rigid plane, while an extremely low FO max valve corresponds to a flexible net for receiving acrobats. The landing mats are required to have a FO-max value as low as possible to ensure a safe landing for gymnasts.
This parameter represents the extent of a cave-in of the mat's portion compressed by the impact. A greater value of S-ein will be effective to decrease the FO-max to a certain degree. However, an excessively great S-ein will render it difficult for the landing gymnasts to control in an instant their posture on the mat. Thus, desired is a combination of the smallest possible S-ein value with the lowest possible FO-max.
This parameter, which is a measure of springback of the mat having received a downward impact, will be expressed in the term of height to which an object having fallen on the mat is repelled upwards thereby. An extremely small S-ruck will disable the safe landing, whereas an excessively great S-ruck repelling the landing gymnasts makes it difficult for them to instantaneously control their posture on the mat. Although a medium S-ruck may be preferred, any value thereof below a certain upper limit will not be regarded, from a practical point of view, as too small to meet the requirements, if FO-max is included in a moderate range.
The FIG short for International Federation of Gymnasts (`Federation Internationale des Gymnastes`) has established the methods of measuring the values of FO-max, S-ein and S-ruck. According to FIG's standard, a landing mat 1000 mm.times.2000 mm wide is prepared for test and 9 (nine) small regions are marked on this mat. A metal column having a diameter of 10 cm and weighing 20 kg will then be dropped 10 (ten) times onto each region from a height of 80 cm thereabove, thus dropping the column 90 (ninety) times in total. 18 (eighteen) data obtained by the first and second droppings of the column are excluded so that only 72 (seventy-two) data are used to calculate an average for the third to tenth droppings for each region.
A standard landing mat for general use in international gymnastic meetings is prescribed by the FIG as shown in Table 1. The parameters FO-max, S-ein and S-ruck for the landing mat 200 mm thick for male gymnasts are: 3650 N (about 372.19 kgf) or less; 110 mm or less; and 120 mm or less, respectively.
Nowadays, many gymnasts are trying a triple somersault or other difficult performances in horizontal bar or other exercises before landing on a mat. Thus, revision of the existing standards for the landing mats has been discussed for a surer protection of gymnasts. The `new` severer standards as listed in Table 1 are going to be adopted by the FIG in the near future.
TABLE 1 ______________________________________ FIG Standards for Landing Mats Thick- ness FO-max (N) S-ein (mm) S-ruck (mm) (mm) Existing New Existing New Existing New ______________________________________ 120 4500 4000 105 105 150 100 150 -- 3500 -- 105 -- 100 180 4050 3000 110 110 185 90 200 3650 3000 110 110 120 90 ______________________________________
3. Prior Art
The landing mat, which the present inventors proposed as disclosed in the Japanese Utility Model Publication No. 4-34845, was approved by the FIG and has widely been employed in international gymnastic meetings.
The prior art landing mat consists of a few or more flat units laid one on another, and each unit comprises a relatively hard top layer and a soft bottom layer fixed thereto. The top layer consists of two strata, that is an upper polyethylene foam whose expansion ratio is 20-40 and a lower polyethylene foam whose expansion ratio is 10-20. The bottom layer is of a thickness equal to or less than that of the top layer, and some flat units of this structure may be stacked one over another to be of a required overall thickness and wrapped with a cover sheet.
This mat is however not in conformity with the new FIG standards. Particularly, the new FO-max standard is not met, thus failing to enhance the gymnasts' safe landing.
In effort to lower the FO-max of the prior art mat, the present inventors tried some new materials to be replaced for those included in said mat. It has been confirmed, that the lower the FO-max value, the more unevenly the mat is depressed upon impact. The mat causing an irregular sinking of feet cannot act as any reliable horizontal plane for gymnasts, forcing them to make a surplus effort to stand still on the mat. In addition, some foot portions of the gymnast will extremely depress some areas of such a mat, almost `colliding` with a hard floor, thus failing to protect him or her from an intolerable shock.